Gateway API: support multiple RequestMirror filters per rule in HTTPRoute [extended]

[sejongk]

Currently, Contour only supports a single RequestMirror filter per rule in HTTPRoute (#4557).
As mentioned in #4557 (comment), we can improve this by supporting multiple RequestMirror filters per rule in HTTPRoute as follows:
If there is more than one RequestMirror filter, then each filter defines a backend to mirror traffic to.
Finally, Contour gets the whole backends, converts these to a slice of MirrorPolicies, and set the slice to dag.Route.MirrorPolicy
ref. https://gateway-api.sigs.k8s.io/v1alpha2/references/spec/#gateway.networking.k8s.io/v1alpha2.HTTPRouteFilter
(Support: Extended)

[sejongk]

Hi, @skriss. I'm tackling this improvement and having an issue with this.

Currently, multiple HTTPRouteFilters with the same type are not supported on the Core/Extended filters(ref. kubernetes-sigs/gateway-api#598).
Therefore, it seems better to change the current HTTPRequestMirrorFilter.backendRef which type is BackendObjectReference into HTTPRequestMirrorFilter.backendRefs which type is []BackendObjectReference in Gateway API.

I'm planning to open a new issue in the gateway-api repository to discuss the above improvement.
Would you mind sharing your idea before I open a new issue for this?

[skriss]

Ah, interesting. In that case, I think this issue can be closed since it's invalid per the current API. If you have a use case for multiple mirror backend refs, then sure, that's worth opening an issue for in the Gateway API repo, but I wouldn't say Contour really has a need for this, we just want to implement the spec fully. For comparison, HTTPProxy only supports a single mirror service.

[skriss]

Closing since per kubernetes-sigs/gateway-api#598, the admission webhook does not allow multiple core filters of a given type per rule.

[sejongk]

@skriss Thanks for the comment!

[skriss]

Reopening this issue, as kubernetes-sigs/gateway-api#2199 has added support for multiple mirror filters per rule. Help wanted! This will be available in Gateway API v0.8.0

[LiorLieberman]

you can assign it to me, already came up with some draft